Well, the truth is I've installed SDDM because of this article. It was interesting for me particulary about why KDM is not going to be used in Wayland environment because it's has been decided to let KDM as it is. KDE decided to not rewrite KDM using QML or creating new from scratch. While kde plasma workspace is going on the way to Wayland, it's just so silly if it doesn't came with any login/display manager.
For some people, not using LightDM is about the license. Again, Canonical seems more and more phenomenon in the opensource world, and I tend to avoid Canonical. I don't like glamour and famous thing, it tends to corrupt or corrupting others. That's why I don't use *ubuntu. Don't argue with me, because I'm not trolling your decision using *ubuntu. For that reason I'm also not using LightDM, but choose SDDM for the display manager, replacing KDM.
Despite it's still immature and very young, the project started about three month ago and still has no stable release, SDDM already have a lot of feature and it's very clean. You can build your own SDDM from git source without any trouble. It only requires Qt4 and PAM. As for me, I have to spamming my Slackware with PAM, but that's easy and I solved it in about an half hour. I just need my old gdm PAM config from here. And I'm able to login into KDE without any problem. I have to say, SDDM is really fast compared to KDM. It's very light and very customable:
As a Wayland aware display manager, SDDM is a good candidate along with LightDM. So, interesting?